Magnetic deflection yoke



Oct. 6-, 1964 F. KRATOCHVIL 3,152,291

MAGNETIC DEFLECTION yoxs Filed March 3. 1961 Fig. I

PRIOR ART 1. 4 y 4 m 5' i0 15 mm 2'0 iNVENTOR Friedrich KraiochviiATTORNEY United States Patent 3,152,291 MAGNETIC DEFLECTION YOKEFriedrich Kratochvii, Hannover-Ricklingen, Germany,

assignor to Telefunken Aktiengeseilschaft, Berlin, Germany Filed Mar. 3,1%1, Ser. No. 93,121 Claims priority, application Germany Mar. 10, 19604 Claims. (Cl. 311-200) The present invention relates to improvements inmagnetic deflection yokes for deflecting the beams of cathode ray tubes,the yokes comprising a ring of ferromagnetic material and sets ofdeflecting coils thereon respectively for horizontal deflection and forvertical deflection.

Prior art means for magnetic deflection of the electron beam of acathode ray tube for television purposes include deflection deviceswherein two saddle coils diametrically oppose one another and havecosine-shaped winding distributions for the deflection of the beam inthe horizontal direction. These coils are arranged within a ring-shapedyoke of ferromagnetic material surrounding the electron beam. Fordeflection of the beam in the vertical direction, two continuously woundtoroidal coils are used which are either wound on the yoke or areslipped thereon after winding. Such a prior-art device is shown inFIGURE 1, wherein the neck 1 of a cathode ray tube is enclosed by aring-shaped yoke 2 of ferromagnetic material on which are arranged twodiametrically opposed continuously wound toroidal coils 3 of such alength that each of these coils overlaps the longitudinal conductorgroups of one saddle coil 4, each respectively, wound with acosine-shaped coil distribution. The longitudinal conductor groups 5 inthis device are shown in cross-section. In this known device, thetoroidal coils 3 are either previously wound on a straight winding coreand subsequently slipped onto the yoke core or are directly wound on theyoke core 2 by means of a winding machine, the feed of the windingmachine being adjusted in such a way that the core is turnedcontinuously and the wound wire always runs radially with respect to thecenter of the ring-shaped yoke. It is also known in such a device towind the toroidal coil in a so-called saw-tooth step wherein the wireafter each completed turn is brought back to the beginning of the coil.It is further known to design the distribution of the coils of thetoroidal winding non-uniformly so as to vary the field distribution ofthis winding.

The invention is based on the problem of improving by simple means thesharpness of the image point when using such windings. Broadly, thisinvention teaches the winding of the toroidal coils in such a way thatthe parts of the coil outside the ring-shaped yoke extend over a smallercircumferential angle than the parts of the coil on the inside of thering-shaped yoke. In a preferred embodiment, the turns of the coil onthe outside of the ring-shaped yoke are bunched together by a U-shapedsupport form.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawings in which:

FIGURE 1 is, as described above, an end view, partly in section, of adeflection yoke according to the prior art.

FIGURE 2 is an illustration of a portion of a deflection yoke accordingto the present invention showing the cross section of one windingthereof.

FIGURES 3 and 4 are graphical illustrations which will be referred to inorder to facilitate an understanding of the following discussion.

Referring now to the drawings, FIGURE 2 shows one half of a ring-shapedyoke core 6, on which there is ion wound a toroidal coil '7. Thistoroidal coil is so dimensioned that the portions 8 of the windingslocated on the outside of the ring-shaped yoke subtend a considerablysmaller circumferential angle 11' than the angle a of portions 3a of thewinding on the inside of the ring-shaped yoke. In the embodiment shownin the drawings, this is accomplished by using a U-shaped form 9 on theoutside of the ring-shaped yoke core 6, between the yoke and the coil 7.In the case where the coil is slipped onto the yoke core 6, it may beadvisable to arrange, at the inside of the winding, a strip of adhesivetape 10 whose ends 11 are wrapped around the sides of the winding tokeep it from spreading. The legs 12 of the U-shaped form 9 may alsoserve as finger levers for the displace ment of the toroidal coilsaround the circumference of the yoke core 6. By this means trapezoidaldistortion, for example, may be compensated for and adjusted. After thecorrect adjustment, the coils may be fixed, for example, by sprayingwith a synthetic resin.

These measures achieve a considerable improvement in the sharpness ofthe image points on the screen, and this improvement can be illustratedwith reference to the diagrams shown in FIGURES 3 and 4.

The point focus b is plotted over a vertical or a horizontal pincushionpattern (S or W) both for the case of a toroidal coil wound according toFIGURE 1 and for a toroidal coil wound according to the invention.Herein, b is understood to be the width of the image point, which in themost favorable case (image point in the center of the screen) is assumedto be Stated as the value for the pincushion distortion is the distanceof the picture raster, measured at the margin, from the shape of arectangle given by the picture corners. A is the curve for a prior-arttoroidal coil according to FIGURE 1; B is a curve for the coil accordingto the invention. With the same point focus, the pincushion distortionfor the known coil is 2 to 3 times as large as that for the coilaccording to the invention (measured under the same electricalconditions). It has been found that the point focus of the luminous spotproduced on the fluorescent screen by the cathode beam gives morefavorable values with circularly-distorting coils than withnon-distorting or cylindrically-distorting coils. Such circulardistortions, however, are intolerable, from the standpoint of theviewer. Up to now, therefore, a compromise always had to be made betweenpoint focus and distortion. As shown by the diagrams in FIGURE 3, theteaching according to the invention makes it possible to improve thepoint focus without thereby affecting the circular distortion in anunfavorable manner. With a coil according to the invention, therefore,the compromise between point focus and distortion may be madeconsiderably more favorable.

If the ratio of circumferential angles 0L and a is chosen in such a waythat the windings all run parallel, the production process may besimplified for making such a coil, and still provide the presentimprovement in the point focus. Because in such a case it is possible towind the coil directly onto the core without having to turn the core forfeeding, production can thereby be rntade considerably more economical.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

1. A magnetic deflection yoke for deflecting the beam of a cathode raytube, comprising, in combination: a ring of ferromagnetic material forsurrounding said beam; at least one set of magnetic deflection windingscompris ing toroidal windings symmetrically spaced and Wound through andon said ring so that the portion of the Winding disposed outside of saidring subtends a smaller circumferential angle as measured from thecenter of the ring than the portion of the Winding passing inside of thering.

2. In a deflection yoke as set forth in claim 1, the ratio of the anglesubtended by the portion of the Winding lying outside the ring-to theangle subtended by the portion of the winding lying inside the ring notexceeding 1:2.

3. In a deflection yoke as set forth in claim 1, a U- shaped forminterposed between the ring and the portion of the winding lying outsideof the ring and having its two legs extending outwardly away from thering and confining the turns of the winding therebetween.

4. In a deflection yoke as set forth in claim 3, said U-shaped formbeing slidable on said ring and said legs serving as hand grips forpositioning the associated wind ing circumferentially of the ring.

References Cited in the file of this patent UNITED STATES PATENTSJanssen Dec. 15, 1959 2,926,273 Haupt et al Feb. 23, 1960

1. A MAGNETIC DEFLECTION YOKE FOR DEFLECTING THE BEAM OF A CATHODE RAYTUBE, COMPRISING, IN COMBINATION: A RING OF FERROMAGNETIC MATERIAL FORSURROUNDING SAID BEAM; AT LEAST ONE SET OF MAGNETIC DEFLECTION WINDINGSCOMPRISING TOROIDAL WINDINGS SYMMETRICALLY SPACED AND WOUND THROUGH ANDON SAID RING SO THAT THE PORTION OF THE WINDING DISPOSED OUTSIDE OF SAIDRING SUBSTENDS A SMALLE CIRCUMFERENTIAL ANGLE AS MEASURED FROM THECENTER OF THE RING THAN THE PORTION OF THE WINDING PASSING INSIDE OF THERING.